The operation of sensors is frequently not easily possible at low temperatures, above all when the environmental temperature drops considerably below freezing point. There is a risk that not all electronic and electromechanical elements used are suitable or licensed for use at low temperatures. In particular optoelectronic sensors are sensitive to fogging at the optical elements, such as lenses or a front screen that may even ice over.
A known solution is the heating of the total device or of its critical components by a heating. The power output of a conventional heating assembly is, however, hardly variable. The accessing of the largely constant heating power practically takes place digitally by a cyclic switching on and off. The desired internal temperature arises by thermal inertia and energetic averaging and the objective is thus reached from a thermal viewpoint.
However, this process demonstrates disadvantages from an electrical viewpoint. The power pick-up differs greatly due to the change of phases having high and low power demands. A lot more than the average power requirement is demanded in the heating phases. The feeding power supply assembly has to be able also to provide the demanded peak powers. This can as a rule only be achieved by a corresponding overdimensioning. The same applies to the required lines, plug connectors and power protection elements within the supply circuit.
DE 199 33 518 B4 discloses a barcode reading device having a heating element whose heat is distributed by the air circulation that a rotating polygon mirror wheel generates. The control of the heating is not discussed.
A barcode reading device is likewise heated in DE 10 2006 054 492 B4, wherein here a heat conductivity body is formed as a reception console for holding the optical or electronic component. In an embodiment, a plurality of heating elements are provided that can be switched centrally by means of a control and regulation unit.
U.S. Pat. No. 6,612,493 discloses a further optical scanner having a heating module that is thermostatically controlled. It is thereby heated as soon as the air temperature drops below a specific value.
U.S. Pat. No. 7,798,411 B2 deals with a front screen for an optical scanner that avoids fogging by means of a PCT (positive temperature coefficient) heating wire. The particular temperature characteristic of the heating wire provides a self-regulation that protects against overheating.